Flask



FIG. 1 is a front perspective view of a flask, according to my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a right side view.

The broken line showing of the atomizer nozzle of the flask is for illustrative purposes only, and forms no part of the claimed design. 

The ornamental design for a flask, as shown and described. 